Modern pre-surgical modeling and planning systems are designed to assist surgeons by allowing them to perform complex tasks such as planing and optimizing tool-paths, manipulatings spaces, excising, harvesting, precisely locating transplantation sites, predicting postoperative results, and others. Such systems are designed to reduce the risks and unknowns in an operating room, and in this regard alone are capable of supplementing the surgeon's own skills and discretion considerably. The focus of much research in this area has been to develop interfaces that can efficiently, effectively, and ergonomically allow surgeons to access volumetric, functional, and trajectory-based navigational data from modeling and planning sessions. The overwhelming thrust of research in the area of surgical modeling and planning understandably has been visually oriented. Recent advances in medical imaging technology (CT, MRI, PET, etc.), coupled with advances in computer-based image processing and modeling capabilities have given physicians an unprecedented ability to visualize anatomical structures in patients, and to use this information in diagnosis and treatment planning. However, visually based systems have proven to have performance problems when running in real-time, which typically renders them unusable except for simulated surgery.
The use of virtual reality in computer-assisted surgical systems is limited in many ways by the present technological level. Thus, for example, limited processing power and real-time rendering places tight constraints on simulations in terms of the sophistication of visually based models. As models become more detailed, more resembling real objects, greater processing power is needed. The head-mounted/heads-up display devices, which are ubiquitous in virtual reality systems are impractical for surgical purposes because they interfere with the surgeon's field of view, and their size and weight produces encumbrance and fatigue. Other factors such as the relatively low scan rates and low resolution further limit the utility of head-mounted display technology for medical use. The devices are discomforting to wear for prolonged periods of time and cause inevitable eyestrain. Furthermore, the latency in image generation and in dynamic head tracking is noticeable in all head-mounted display systems, but is most strikingly apparent in heads-up systems where synthetic imagery is overlaid over the real-world visage.
The implications for computer-assisted surgery based solely on visual processing are disappointing. It is simply unacceptable for the surgeon's speed of motion during an operation to be limited by the demands of the technology. The ultimate goal, after all, is for the technology to remove limitations rather than impose them. Poorly conceived human-machine interface design adversely affects the ability of surgeons to successfully perform procedures. This is unfortunately the case with many virtual reality systems which entangle the surgeon with sensors and instrumentation. Ergonomic design must be a requirement of any system used in the operating room because many parameters already interfere with the intentions of the surgeon and the execution of those intentions by assisting devices. The limitations of the technology should not be further degraded by the interposition of poorly configured interfaces. Technology used in the operating room cannot only be useful in itself, but must be intuitively useable in order to be functionally useful.
Another different but very important limitation of the commercially available technology is that the precision of image-based pre-surgical planning often greatly exceeds the precision of actual surgical execution. In particular, precise surgical execution has been limited to procedures, such as brain biopsies, in which a suitable stereotactic frame is available. The inconvenience and restricted applicability of such a frame or device has led many researchers to explore the use of robotic devices to augment a surgeon's ability to perform geometrically precise tasks planned from computed tomography (CT) or other image data. Clearly the ultimate goal of this research is a partnership between a human and machines (such as computers and robots), which seeks to exploit the capabilities of both, to do a task better than either can do alone. Clearly, computers can be very precise and can process large volumes of data coming from any number of sensory feedback devices. On the other hand, a human surgeon is very dexterous, strong, fast, and is highly trained to exploit a variety of tactile, visual, and other cues. "Judgementally" controlled, the surgeon understands what is going on in the surgery and uses his dexterity, senses, and experience to execute the procedure. However, in order to increase precision within acceptable time limits or with sufficient speed, humans must be willing to rely on machines to provide the precision.
U.S. Patents such as U.S. Pat. Nos. 5,546,943; 5,513,991; 5,445,566; 5,402,801 and 4,905,163 discuss various devices which can be used to assist the surgeon's work. However, none of the prior art discusses in a coherent way the use of another information channel, the human auditory system, for the accurate processing by the surgeons of the huge volume of information generated during an operation.
There exist a number of significant advantages to incorporating audio feedback techniques into applications intended for real-time surgical use. The computational requirements for generating an audio signal are substantially smaller than for graphics, even though the auditory sensory modality is comparatively rich in bandwidth. Because auditory perception is omnidirectional, it is possible to localize sounds emitted from any point in space, even from behind objects, whereas with vision it is only possible to localize objects falling within the viewing frustum. Sound is capable of relating information about the relative distance, azimuth, elevation, and the velocity of a sound source through amplitude, spectral composition and Doppler shifting, respectively. With advanced techniques such as three-dimensional filtering, audio windowing and room acoustic simulation, it is also possible to relate the orientation of objects within a synthetic acoustic space. These observations suggest that the area of information transmission in user interfaces need not be constrained to the size of the monitor or head-mounted display used. Information can emanate from anywhere in space. The fact that audio feedback technology avoids many of the shortcomings of visual systems has already made it an attractive area of exploration.
For example, it has been established that audio feedback can extend the available information transmission bandwidth significantly, in part because humans are capable of processing audio information in parallel. The vertigo caused by rendering latency and scanning, eyestrain, and various etiologies of simulator sickness almost universal in binocular three dimensional systems are not an issue in audio systems.
Accordingly, it is perceived that audio-based real-time intraoperative systems can considerably enhance the utility of modeling and planning technology to surgeons who cannot tolerate the encumbrance of graphical display hardware, and whose visual faculties have preexisting obligations. Presently available systems inadequately exploit these advantages of an independent or supplementary audio feedback system. Therefore, there is a need for a computer system and method for position guidance using audio feedback providing spatial information.